Electroless copper plating solution

ABSTRACT

An object is to provide an electroless copper plating solution with excellent solution stability and easy composition control while being used in a neutral range. To achieve the object, a reducing electroless copper plating solution used in a neutral range is employed that contains a copper salt serving as a copper ion supply source, a complexing agent for chelating copper ions, a reducing agent, a surfactant, an aromatic compound containing nitrogen, and contains a tellurium compound serving as a deposition stabilizer, and that has a solution pH of 6 to 9.

TECHNICAL FIELD

The present application relates to an electroless copper plating solution, particularly to a reducing electroless copper plating solution used in a neutral range.

BACKGROUND ART

Conventionally, an electroless copper plating solution has been employed that uses formaldehyde as a reducing agent for copper ions. However, formaldehyde has an irritating odor that deteriorates the working environment and causes adverse effects on the human body. Furthermore, the electroless copper plating solution using formaldehyde is strongly alkaline, and thus the use of the electroless copper plating solution is difficult especially when the object to be plated is aluminum, aluminum alloy, or the like.

Therefore, it has been studied to use a borane compound in place of formaldehyde as a reducing agent. Due to the excessive reducing power, however, there have been problems such as the reductive deposition of metal on a wall surface or the like of a plating tank and the low stability of a plating solution due to the deposition of metal components over time.

To solve such problems, an electroless copper plating solution as disclosed in Patent Literature 1 has been proposed. This Patent Literature 1 discloses “an electroless copper plating bath having a pH of 4 to 9, containing a water-soluble copper salt, amino borane or a substituted derivative thereof as a reducing agent, and no formaldehyde, the electroless copper plating bath containing polyaminopolyphosphonic acid as a complexing agent, an anionic surfactant, an antimony compound, and a nitrogen-containing aromatic compound”.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Laid-Open No. 2013-234343

SUMMARY OF INVENTION Technical Problem

However, the following problems have been pointed out in the electroless copper plating bath disclosed in Patent Literature 1: the first problem is that if the electroless copper plating bath disclosed in Patent Literature 1 is left in a plating bath for a long time after use, copper tends to deposit on the bottom of the bath, stirring jigs, and the like, resulting in a high tendency to have a lack of solution stability as a plating solution; the second problem is that an electroless copper plating layer formed using the electroless copper plating bath disclosed in Patent Literature 1 tends to have a non-uniform appearance; and the third problem is that when plating is performed on an aluminum material using the electroless copper plating bath disclosed in Patent Literature 1, the copper plating layer tends to swell even if the aluminum itself is not damaged, resulting in a tendency for pits to occur.

Although the above problems have been pointed out in the market, in the use of the electroless copper plating bath disclosed in Patent Literature 1, the control range of proper composition is narrow, and solution stability is poor, which probably makes it difficult to achieve operational stability in plating.

Accordingly, an object of the present application is to provide an electroless copper plating solution with excellent solution stability and easy composition control, which does not cause the above-mentioned problems.

Solution to Problem

As a result of intensive studies, the inventors of the present application have conceived of employing the following formaldehyde-free electroless copper plating solution. The summary of the invention of the electroless copper plating solution according to the present application will be described below.

The electroless copper plating solution according to the present application is a reducing electroless copper plating solution used in a neutral range that contains a copper salt serving as a copper ion supply source, a complexing agent for chelating copper ions, a reducing agent, a surfactant, an aromatic compound containing nitrogen, and contains a tellurium compound serving as a deposition stabilizer, and that has a solution pH of 6 to 9.

In the electroless copper plating solution according to the present application, the tellurium compound serving as a deposition stabilizer is preferably used in a concentration range of 0.1 mg/L to 100 mg/L in terms of tellurium.

In the electroless copper plating solution according to the present application, the complexing agent for chelating copper ions is preferably a phosphonic acid-based chelating agent is used in a concentration range of 0.1 to 10 times the number of moles of copper.

In the electroless copper plating solution according to the present application, the reducing agent is preferably amine borane or a derivative thereof.

In the electroless copper plating solution according to the present application, the surfactant is preferably an anionic surfactant used in a concentration range of 0.01 mg/L to 1500 mg/L.

In the electroless copper plating solution according to the present application, the aromatic compound containing nitrogen is preferably used in a concentration range of 0.01 mg/L to 1000 mg/L.

Advantageous Effects of Invention

The electroless copper plating solution according to the present application contains a tellurium compound serving as a deposition stabilizer for the electroless copper plating solution, thereby dramatically improving the solution stability as a plating solution even though it is used in a neutral range without containing formaldehyde. As a result, a change in the composition of the plating solution during plating operation is small, a stable copper plating layer can be formed even if the composition is slightly changed, and it becomes possible to obtain layer thickness uniformity and uniform appearance quality of the copper plating layer. Then, even if the electroless copper plating solution is left in the plating tank after the plating operation, unnecessary copper deposition does not occur while a plating solution is less deteriorated, making it possible to prolong the life of the solution. Furthermore, by employing the electroless copper plating solution in the neutral range according to the present application, aluminum itself is not damaged when the solution is plated on an aluminum material, and plating defects such as blisters and pits in the plating layer can be efficiently eliminated.

DESCRIPTION OF EMBODIMENTS

Embodiments of the electroless copper plating solution according to the present application and electroless copper plating methods using the same will be described below.

A. Embodiments of Electroless Copper Plating Solution

The electroless copper plating solution according to the present application is an electroless copper plating solution used in a neutral range, and this electroless copper plating solution contains a tellurium compound serving as a deposition stabilizer in terms of a component and has a solution pH of 6 to 9. The solution pH of the electroless copper plating solution will be described below, and then each component will be described.

Solution pH: The solution pH is preferably 6.0 to 9.0. When the solution pH is less than 6.0, the electroless copper plating solution is in an acidic range, which is not preferable because the effect of components such as the reducing agents described below is likely to decrease, making it difficult to prolong the life of the electroless copper plating solution. On the other hand, when the solution pH is more than 9.0, the electroless copper plating solution is in an alkaline range, which is not preferable because the surface of the object to be plated, such as an aluminum material or a ceramic material, is more likely to be damaged. Here, the solution pH is more preferably 6.5 to 8.5, which is even closer to neutral, and in this case, the damage to the object to be plated can be prevented more reliably.

As a pH adjusting agent when the solution pH of the electroless copper plating solution according to the present application needs to be adjusted, hydrochloric acid, sulfuric acid, or the like may be used to adjust the solution pH to the acid side while sodium hydroxide, potassium hydroxide, or the like may be used to adjust the solution pH to the alkali side.

Deposition stabilizer: In the electroless copper plating solution according to the present application, the tellurium compound serving as a deposition stabilizer is used. Examples of the tellurium compound include any one or more of telluric acid and a salt thereof, tellurous acid and a salt thereof, tellurium dioxide, tellurium trioxide, tellurium chloride, and dimethyl telluride. By using these tellurium compounds, all of the problems that have not been solved in the past can now be solved. In other words, the solution stability is dramatically improved by using a tellurium compound serving as a deposition stabilizer in the electroless copper plating solution, and thus the plating solution can be easily managed. At the same time, the deposition state during the formation of a copper plating layer is also stable, making it possible to form a good copper plating layer.

The tellurium compound serving as a deposition stabilizer is preferably contained in the electroless copper plating solution in a concentration range of 0.1 mg/L to 100 mg/L in terms of tellurium. When the content of the tellurium compound is less than 0.1 mg/L in terms of concentration of tellurium, the solution stability of the electroless copper plating solution cannot be improved, the lifetime extension of the plating solution cannot be achieved, and the characteristics of the plating solution vary due to the change in the composition, making it difficult to use the electroless copper plating solution for a long time, which is not preferable. On the other hand, when the content of the tellurium compound is more than 100 mg/L in concentration as tellurium, the phenomenon that copper deposition is markedly reduced is observed, which is not preferable because rapid copper plating layer formation becomes difficult. From the viewpoint of reliably ensuring the stability of the copper deposition rate, therefore, the content of the tellurium compound is more preferably in the concentration range of 0.3 mg/L to 70 mg/L in terms of concentration of tellurium. In order to ensure the effect of the addition of the tellurium compound, and minimize the variation in the formation rate of the copper plating layer, the tellurium compound is most preferably contained in the concentration range of 0.5 mg/L to 50 mg/L in terms of tellurium.

Copper ion supply source: The copper salt serving as a copper ion supply source is used in the electroless copper plating solution according to the present application. Examples of the copper salt include any one or more of water-soluble copper salts such as copper sulfate, copper nitrate, copper chloride, copper acetate, copper citrate, copper tartrate, copper gluconate, and hydrates thereof. As described above, two or more copper salts of the present application can be simultaneously used in combination, and there is no particular limitation on the mixing ratio of two or more copper salts as long as the amount of copper ions is in the following range. Considering the conditions such as raw material cost and wastewater load, it is preferable that the most widely available is copper sulfate (copper sulfate pentahydrate) or a combination of copper sulfate and copper hydrochloride.

In the electroless copper plating solution according to the present application, the content of the copper salt is preferably in the concentration range of 0.01 mol/L to 1 mol/L in terms of concentration of copper. When the content of the copper salt in the electroless copper plating solution according to the present application is less than 0.01 mol/L in terms of concentration of copper because the copper deposition rate is remarkably decreased, the time required for operation becomes long, and the productivity required for industrial purposes cannot be obtained, which is not preferable. On the other hand, even if the content of copper salt is more than 1 mol/L in terms of concentration of copper, the copper deposition rate is not improved, but rather the appearance defects of the formed copper plating layer tend to increase, which is not preferable. From the viewpoint of reliably ensuring the appearance quality of the copper plating layer to be formed, therefore, the content of the copper salt is preferably in the concentration range of 0.02 mol/L to 0.5 mol/L in terms of concentration of copper.

Complexing agent: The electroless copper plating solution according to the present application is used in the neutral range, and it is preferable to use a phosphonic acid-based chelating agent as the complexing agent. This is because the phosphonic acid-based chelating agent easily forms a complex of copper ions in the neutral range. The phosphonic acid-based chelating agent includes 1-hydroxyethane-1,1-diphosphonic acid, N,N,N′,N′-ethylenediaminetetrakis(methylenephosphonic acid), nitrilotris(methylenephosphonic acid), diethylenediaminepenta(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), bis(hexamethylenetriaminepenta(methylenephosphonic acid)), glycine-N,N-bis(methylenephosphonic acid), and salts thereof, and one or more of them can be used simultaneously.

Since the complexing agent chelates copper ions, the amount of the complexing agent added is determined by the copper content in the electroless copper plating solution. In the electroless copper plating solution according to the present application, the phosphonic acid-based chelating agent as a complexing agent is preferably used in a concentration range of 0.1 to 10 times the number of moles of copper in the electroless copper plating solution. When the concentration of the phosphonic acid-based chelating agent is less than 0.1 times the number of moles of copper, copper ions cannot be sufficiently complexed, and solution stability as an electroless copper plating solution cannot be ensured, which is not preferable. On the other hand, when the concentration of the phosphonic acid-based chelating agent is more than 10 times the number of moles of copper, the amount of the chelating agent is more than the amount required for the complexation of copper ions, which is not preferable because it wastes resources and also causes the appearance quality of the copper plating layer to deteriorate.

Reducing agent: Various reducing agents can be used for copper ions. In the case of the electroless copper plating solution according to the present application, however, since it is used in the neutral range, it is preferable to use amine borane or a derivative thereof as a reducing agent usable in the neutral range in order to ensure the solution stability. More specifically, any one or more of dimethylamine borane, diethylamine borane, tert-butylamine borane, triethylamine borane, trimethylamine borane, and the like can be used. The concentration of this reducing agent is not particularly limited, but it is reasonable to set the concentration in the range of 0.01 mol/L to 0.5 mol/L. When the concentration of the reducing agent is less than 0.01 mol/L, the copper deposition rate is slow, which is not preferable. On the other hand, when the concentration of the reducing agent is more than 0.5 mol/L, it is not preferable because the copper deposition rate does not increase and is simply a waste of resources.

Surfactant: In the electroless copper plating solution according to the present application, it is preferable to use a surfactant for the purpose of improving the solution stability and improving the layer thickness uniformity and appearance quality of the plating layer to be formed. Especially in the case of an electroless copper plating solution used in the neutral range, it is preferable to use an anionic surfactant.

As the anionic surfactants, all the surfactants which are called “anionic surfactants” or “anionic surface-active agents” in the market can be used. Examples include any one or more of alkylcarboxylic acid-based surfactants, naphthalene sulfonate formaldehyde condensates such as sodium salts of β-naphthalene sulfonate formalin condensate, polyoxyalkylene ether sulfates such as sodium polyoxyethylene lauryl ether sulfate and triethanolamine polyoxyethylene alkyl ether sulfate, and sodium dodecyl sulfate, but not special limitations are required.

The concentration of the surfactant is not particularly limited, but it is reasonable to set the concentration in the range of 0.01 mg/L to 1500 mg/L. When the concentration of the surfactant is less than 0.01 mg/L, it is not preferable since the solution stability of the electroless copper plating solution does not improve, making it difficult to prolong the life of the plating solution, and the appearance quality of the copper plating layer tends to deteriorate. On the other hand, when the concentration of the surfactant is more than 1500 mg/L, there is no particular problem, but the solution stability is not further improved nor the appearance quality is improved. Besides, the bath control during the plating operation becomes complicated, which is not preferable.

Aromatic compound containing nitrogen: In the electroless copper plating solution according to the present application, an aromatic compound containing nitrogen (so-called a heterocyclic aromatic compound containing nitrogen) is used to stabilize copper deposition in electroless copper plating. Examples of the nitrogen-containing aromatic compounds include any one or more of: imidazole or substituted derivatives thereof; pyrazole or substituted derivatives thereof; oxazole or substituted derivatives thereof; thiazole or substituted derivatives thereof; pyrazine or substituted derivatives thereof; pyridazine or substituted derivatives thereof; triazine or substituted derivatives thereof; benzothiazole or substituted derivatives thereof; pyridines such as pyridine, 2,2′-dipyridyl, 4,4′-dipyridyl, nicotinic acid, nicotinamide, picolines, and lutidines, or substituted derivatives thereof; quinolines such as quinoline and hydroxyquinoline, or substituted derivatives thereof; acridines such as acridine, 3,6-dimethylaminoacridine, proflavine, acridine acid, and quinoline-1,2-dicarboxylic acid, or substituted derivatives thereof; pyrimidines such as pyrimidine, uracil, uridine, thymine, 2-thiouracil, 6-methyl-2-thiouracil, and 6-propyl-2-thiouracil, or substituted derivatives thereof; and phenanthrolines such as 1,10-phenanthroline, neocuproine, and bathophenanthroline, or substituted derivatives thereof; and purines such as purine, aminopurine, adenine, adenosine, guanine, hydantoin, xanthine, hypoxanthine, caffeine, theophylline, theobromine, and aminophylline, or substituted derivative thereof.

The concentration of the aromatic compound containing nitrogen that is contained in the electroless copper plating solution according to the present application is preferably 0.01 mg/L to 1000 mg/L. When the concentration of the aromatic compound containing nitrogen is less than 0.01 mg/L, the effect as a deposition stabilizer for copper cannot be exhibited, which is not preferable because the appearance of the formed copper plating layer is also impaired. On the other hand, when the concentration of the aromatic compound containing nitrogen is more than 1000 mg/L, the solution stability of the electroless copper plating solution becomes excessive, which is not preferable because it causes a decrease in the copper deposition rate and an undeposited portion of the plating layer is generated.

B. Electroless Copper Plating Method

Regarding the electroless copper plating method, conventionally known electroless plating methods and conditions may be applied using the above-mentioned electroless copper plating solution. Therefore, it is considered unnecessary to describe the electroless copper plating method in detail here, and the electroless plating methods and conditions are described in Example.

Although the electroless copper plating solution according to the present application has been described above, the present application will be described in more detail below with reference to Examples and Comparative Examples of the present application. Note that the present application is not limited to these examples at all.

Example 1

In Example 1, the solution stability as a plating solution was confirmed after electroless copper plating was performed using an electroless copper plating solution containing a copper salt serving as a copper ion supply source, a complexing agent for chelating copper ions, a reducing agent, a surfactant, an aromatic compound containing nitrogen, and containing a tellurium compound serving as a deposition stabilizer, and having a solution pH of 7.7 and a solution temperature of 60° C. Here, the evaluation of the solution stability as a plating solution is indicated by “◯” when no deposition was observed on a part other than the object to be treated, by “Δ” when the deposition was slightly observed, and by “X” when the deposition was remarkably or decomposition of the plating solution occurred during plating, after the electroless copper plating solution is heated and plated while keeping the solution temperature constant, and then the electroless copper plating solution is left for 12 hours. The results of this confirmation are shown in Table 3 below.

In Example 1, a substrate with an aluminum circuit (hereinafter simply referred to as a substrate), an object to be plated, was subjected to pretreatment under the conditions listed in Table 1 below (in the order from the top in the table), and then immersed in an electroless copper plating solution for 120 minutes to perform electroless copper plating, thereby forming a copper plating layer on the surface of the aluminum circuit pattern.

TABLE 1 Treatment Treatment step Name of bath condition Degreasing Melcleaner SC-7001 70° C., 30 secs Etching Melplate E-7121 70° C., 30 secs Conditioning Melplate Conditioner 7230 22° C., 20 secs Single zincate treatment Melplate FZ-7350 22° C., 20 secs Zinc stripping 20 wt % nitric acid 22° C., 10 secs Double zincate treatmen Melplate FBZ 22° C., 30 secs

In Example 1, an electroless copper plating solution having the composition shown below was prepared.

(Electroless Copper Plating Solution Composition)

-   -   Copper salt (copper sulfate pentahydrate): 0.06 mol/L (4 g/L in         terms of concentration of copper)

Complexing Agent

-   -   (ethylenediaminetetra(methylenephosphonic acid)): 0.08 mol/L     -   Reducing agent (dimethylamine borane): 0.09 mol/L     -   Surfactant (sodium dodecyl sulfate): 20 mg/L     -   Aromatic compound containing nitrogen (1,10-phenanthroline): 4         mg/L     -   Deposition stabilizer (sodium tellurate): 1 mg/L (in terms of         concentration of tellurium)

In Example 1, the deposition rate of the electroless copper plating layer, the plating appearance, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the copper plating layer after the plating layer was formed on the surface of the aluminum circuit pattern (hereinafter, also simply referred to as a pattern) on the substrate were confirmed. Note that the above-mentioned “presence or absence of undeposition in pattern” indicates whether or not an undeposited portion of the copper plating layer is generated on the surface of the aluminum circuit pattern. Here, the deposition rate of the electroless copper plating layer was determined by measurement with a fluorescent X-ray film thickness gauge. In addition, the plating appearance was visually evaluated (“◯” for the uniform plating appearance and “X” for the uneven plating appearance). The results of these confirmations are shown in Table 3 as well.

Example 2

In Example 2, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 2, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “2 mg/L” in terms of concentration of tellurium. Accordingly, the description of the conditions for the electroless copper plating in Example 2 is omitted.

Example 3

In Example 3, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 3, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “10 mg/L” in terms of concentration of tellurium. Accordingly, the description of the conditions for the electroless copper plating in Example 3 is omitted.

Example 4

In Example 4, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 4, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “20 mg/L” in terms of concentration of tellurium. Accordingly, the description of the conditions for the electroless copper plating in Example 4 is omitted.

Example 5

In Example 5, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 5, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “50 mg/L” in terms of concentration of tellurium. Accordingly, the description of the conditions for the electroless copper plating in Example 5 is omitted.

Example 6

In Example 6, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 6, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “5 mg/L” in terms of concentration of tellurium and the solution pH was changed to 6.5. Accordingly, the description of the conditions for the electroless copper plating in Example 6 is omitted.

Example 7

In Example 7, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 7, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “5 mg/L” in terms of concentration of tellurium and the solution pH was changed to 7.0. Accordingly, the description of the conditions for the electroless copper plating in Example 7 is omitted.

Example 8

In Example 8, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 8, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “5 mg/L” in terms of concentration of tellurium and the solution pH was changed to 8.0. Accordingly, the description of the conditions for the electroless copper plating in Example 8 is omitted.

Example 9

In Example 9, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 9, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “5 mg/L” in terms of concentration of tellurium and the solution pH was changed to 8.5. Accordingly, the description of the conditions for the electroless copper plating in Example 9 is omitted.

Comparative Example 1

In Comparative Example 1, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Comparative Example 1, the electroless copper plating was performed under the same conditions as in Example 1, except that “antimony oxide” was used in place of sodium tellurate as a deposition stabilizer in the electroless copper plating solution composition in order to compare with Examples 1 to 9, the content thereof was set at 4 mg/L in terms of concentration of antimony, and the concentration of the reducing agent was set at 0.14 mol/L. Accordingly, the description of the conditions for the electroless copper plating in Comparative Example 1 is omitted.

Comparative Example 2

In Comparative Example 2, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Comparative Example 2, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition, was changed to “0 mg/L (i.e., no sodium tellurate)” in terms of concentration of tellurium in order to compare with Examples 1 to 9. Accordingly, the description of the conditions for the electroless copper plating in Comparative Example 2 is omitted.

Comparative Example 3

In Comparative Example 3, the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Comparative Example 3, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “200 mg/L” in terms of concentration of tellurium in order to compare with Examples 1 to 9. Accordingly, the description of the conditions for the electroless copper plating in Comparative Example 3 is omitted.

Here, for ease of understanding, the compositions of the electroless copper plating solutions used in Examples and Comparative Examples are listed in Table 2.

TABLE 2 Composition and conditions Aromatic compound Copper Complexing Reducing containing Deposition Solution salt agent agent Surfactant nitrogen stabilizer Solution temperature Sample (mol/L) (mol/L) (mol/L) (mg/L) (mg/L) (mg/L) pH (° C.) Example 1 0.06 0.08 0.09 20 4 1 7.7 60 2 0.06 0.08 0.09 20 4 2 7.7 60 3 0.06 0.08 0.09 20 4 10  7.7 60 4 0.06 0.08 0.09 20 4 20  7.7 60 5 0.06 0.08 0.09 20 4 50  7.7 60 6 0.06 0.08 0.09 20 4 5 6.5 60 7 0.06 0.08 0.09 20 4 5 7.0 60 8 0.06 0.08 0.09 20 4 5 8.0 60 9 0.06 0.08 0.09 20 4 5 8.5 60 Comparative 1 0.06 0.08 0.14 20 4   4 * 7.7 60 Example 2 0.06 0.08 0.09 20 4 0 7.7 60 3 0.06 0.08 0.09 20 4 200  7.7 60 * Use of “antimony oxide” as a deposition stabilizer (with a content of 4 mg/L in terms of concentration of antimony)

The confirmation results of the tests conducted as Examples and Comparative Examples are shown in Table 3.

TABLE 3 Confirmation results Depo- Out-of- sition Plating pattern Undepo- rate appear- depo- sition in Solution Sample (μm/h) ance sition pattern stability Example 1 3.9 ◯ Absent Absent ◯ 2 4.3 ◯ Absent Absent ◯ 3 5.4 ◯ Absent Absent ◯ 4 5.2 ◯ Absent Absent ◯ 5 4.3 ◯ Absent Absent ◯ 6 1.0 ◯ Absent Absent ◯ 7 2.6 ◯ Absent Absent ◯ 8 10.0 ◯ Absent Absent ◯ 9 10.7 ◯ Absent Absent ◯ Compar- 1 6.1 X Absent Present X ative 2 2.0 X Present Absent Δ Example 3 Undepo- — — — ◯ sited

(Results and Evaluation)

From the confirmation results shown in Table 3, Examples 1 to 9 gave good results in all of “plating appearance”, “out-of-pattern deposition”, “undeposition of pattern”, and “solution stability”. On the other hand, as in Comparative Example 1, when antimony was contained instead of tellurium as a deposition stabilizer in the electroless copper plating solution, a decrease in solution stability was observed. Furthermore, in Comparative Example 1, the plating layer was not formed sufficiently on the surface of the aluminum circuit pattern on the substrate, nor was the plating appearance uniform. When the concentration of tellurium in the deposition stabilizer was less than 0.5 mg/L, as in Comparative Example 2, deteriorated plating appearance and solution stability was also observed as. In Comparative Example 2, a protrusion from the pattern was further observed. When the concentration of tellurium in the deposition stabilizer was more than 100 mg/L, as in Comparative Example 3, almost no plating was deposited, and thus the plating layer was not formed on the surface of the aluminum circuit pattern on the substrate.

Based on the above, it was found that a change in the composition of the plating solution during plating operation is small and a stable copper plating layer can be formed even if the solution is a reducing electroless copper plating solution used in the neutral range without containing formaldehyde by satisfying the conditions of the present application, “containing a copper salt serving as a copper ion supply source, a complexing agent for chelating copper ions, a reducing agent, a surfactant, an aromatic compound containing nitrogen, and containing a tellurium compound serving as a deposition stabilizer, and having a solution pH of 6 to 9”.

INDUSTRIAL APPLICABILITY

The electroless copper plating solution according to the present application is used in a neutral range and does not cause damage to an object to be plated. Therefore, the electroless copper plating solution is usable in the object to be plated such as an aluminum material or a ceramic material, which is easily damaged. In addition, since the electroless copper plating solution has a long life and excellent solution stability, the running cost of electroless copper plating can be reduced. 

1. A reducing electroless copper plating solution used in a neutral range, comprising a copper salt serving as a copper ion supply source, a complexing agent for chelating copper ions, a reducing agent, a surfactant, an aromatic compound containing nitrogen, wherein the complexing agent for chelating copper ions is a phosphonic acid-based chelating agent, wherein the reducing agent is amine borane or a derivative thereof, and comprising a tellurium compound serving as a deposition stabilizer is used in a concentration range of 0.1 mg/L to 100 mg/L in terms of tellurium, and having a solution pH of 6 to
 9. 2. The electroless copper plating solution according to claim 1, wherein the tellurium compound serving as a deposition stabilizer is at least one selected from the group consisting of telluric acid and a salt thereof, tellurous acid and a salt thereof, tellurium dioxide, tellurium trioxide, tellurium chloride, and dimethyl telluride.
 3. The electroless copper plating solution according to claim 1, wherein the phosphonic acid-based chelating agent is used in a concentration range of 0.1 to 10 times the number of moles of copper in the electroless copper plating solution.
 4. The electroless copper plating solution according to claim 1, wherein the reducing agent is at least one selected from the group consisting of dimethylamine borane, diethylamine borane, tert-butylamine borane, triethylamine borane, trimethylamine borane.
 5. The electroless copper plating solution according to claim 1, wherein the surfactant is an anionic surfactant used in a concentration range of 0.01 mg/L to 1500 mg/L.
 6. The electroless copper plating solution according to claim 1, wherein the aromatic compound containing nitrogen is used in a concentration range of 0.01 mg/L to 1000 mg/L. 